1. Field of the Invention
The present invention relates to the formation of field windings for dynamo-electric machines and, more particularly, relates to the efficient formation of layered windings in stators having skewed slots.
2. Description of Related Prior Art
Many conventional dynamo-electric machines include a stator core formed by a plurality of stacked thin laminations of magnetically permeable material defining a central bore for receiving a rotor member of the machine. The stator core typically includes a plurality of slots extending radially from the central bore and defined by radially extending teeth. Field coils of the machine are positioned on the teeth of the stator core and are formed by insulated wire conductor wound around each of the teeth, or around predetermined groups of teeth, a predetermined number of turns.
The field coils are generally applied to the stator by either preforming the coils and pushing them through the slots onto the stator teeth, or by winding the wire directly onto the stator teeth, which may be accomplished by a winding machine. Winding machines for winding wire onto stators have been used for many years and generally include a winding head mounted on the end of a shuttle and positioned in axial alignment with the bore of a stator. The shuttle is sequentially reciprocated and oscillated in a cyclic manner to move the winding head through the bore of the stator in order to position the wire for the coils in the slots of the stator. The wire is drawn or pulled from the winding head in response to its movement relative to the stator, and the winding head is typically provided with a radially extending needle which is adapted to properly radially position the wire within the slots and around the ends of the teeth of the stator.
Existing winding machines have generally controlled the movement of the winding head by using a combination of cams and gears to effect the desired reciprocating and oscillating movement. Further, such machines are for the most part designed to perform a winding operation on only stators having straight slots, as opposed to skewed slot stators. Typical prior art winding machines are illustrated in U.S. Pat. Nos. 3,338,526, 3,493,186 and 3,524,600.
In an improvement on stator winding machines for winding stators having straight slots, U.S. Pat. No. 3,539,121 discloses a machine for winding stators with skewed slots. This machine is provided with a skewed cam for guiding a roller connected to the shuttle wherein the skewed cam is shaped in accordance with the slots of the stator to be wound. Accordingly, although this machine discloses a mechanism for winding skewed stators, a specially shaped cam must be provided for each particular stator configuration to enable the spindle to follow the shape of the stator slots. Also, an additional mechanism is required to oscillate the shuttle as it reaches the ends of the slots such that the movements of the shuttle are provided through a relatively complex combination of mechanisms.
A problem associated with conventional winding machines, and in particular when forming coils for stators having skewed slots, is the positioning of the wire within the slot in such a manner that a minimum of wire is used to form the desired number of coil turns. As a result of drawing the wire from the winding head in tension as it is wound around the stator teeth, the positioning of the wire has in the past been relatively imprecise such that obtaining of uniform wire layers has heretofore been extremely difficult if not impossible with existing winding techniques and machinery. Further, the existing techniques for winding stators having skewed slots do not permit for placement of the winding wire in a predetermined layered pattern to maximize the efficient use of the winding wire and thereby decrease the overall cost of the wound stator.